The molecular mechanisms involved in DNA replication are being studied. Proteins involved in both phage lambda and E. coli replication are being purified and studied in vitro for their interactions with each other and with DNA. Attempts are being made to reproduce in vitro, the in vivo pathway of replication of lambda DNA in extracts of phage infected bacteria supplemented with phage replication proteins. The present emphasis is to gain insight into the process of initiation of chromosome replication.